The invention relates generally to measuring, monitoring, analyzing, recording and communicating electrical power system parameters. The invention further relates to the use of a trigger signal from a monitoring device to initiate power system waveform capture at a plurality of points in the power system. The invention also relates to the simultaneous storage of the power system waveform data.
Power system parameters are measured, analyzed and recorded for the purpose of system evaluation and planning. Waveform analysis, including harmonic analysis, is often performed on power system waveforms to determine the root cause of power system anomalies. Measured data is also used to calculate real power, reactive power, energy consumption and the like.
Generally, power system parameters are measured at various points throughout the power system by individual power system monitoring devices. Often the monitoring devices are interconnected via a communication network and integrated into a power management system. The power management system control unit coordinates network communication. Additionally, the control unit allows the user to retrieve data from each of the monitoring devices. However, the communication speed of power management systems is relatively slow because there is no direct monitoring device to monitoring device trigger communication and the control unit must periodically poll each device for data.
State of the art monitoring devices include an internal trigger that initiates a waveform capture when one or more power system parameter deviates outside predetermined values. Power system analysis is most effective when the user can evaluate data simultaneously recorded at multiple points in the power system. However, state of the art monitoring devices cannot provide this data because they do not generate shared trigger signals.
In one approach, manufacturers rely on power management control units to provide a common external trigger signal to initiate simultaneous waveform capture in multiple monitoring devices. However, this approach is deficient because the signal is sent over the communication network hence its speed is limited by the speed of the system and the amount of data being communicated.
The system response time is delayed further when a monitoring device identifies a trigger event but a control unit issues the common trigger signal. Where waveform capture is event triggered the waveform capture doesn""t occur until the monitoring device communicates data to the control unit, the data is processed by the control unit and a trigger signal is communicated back to the monitoring devices. The added communication and processing performed by the control unit delays the waveform capture. Additionally, multiple monitoring device waveform capture will not be initiated when there is a problem with control unit operation.
In a second approach, each capturing device internally triggers a waveform capture where a common electrical condition is sensed by multiple devices. This approach is deficient because all devices may not be triggered by the fault due to sensitivity of settings and differences in electrical appearance of the fault at different locations. Today, the time synchronization precision of many communication protocols is inadequate to assure that captured events stored in multiple devices are properly associated with an electrical condition common to all.
It is therefore advantageous to design a circuit monitoring system having direct montoring device to monitoring device trigger communication. It is also seen to be desirable to provide substantially simultaneous waveform capture independent of a control unit thereby increasing waveform capture reliability, speed and synchronization among multiple monitoring devices. Further advantages are provided when the preceding features can be retrofitted to existing systems and devices.
Accordingly, the present invention provides a plurality of monitoring devices capable of performing a waveform capture following generation of an internal trigger signal or upon receipt of an external trigger signal communicated directly from another monitoring device in the network. Monitoring devices are also capable of generating an external trigger signal and communicating the signal directly to other monitoring devices to initiate a simultaneous waveform capture.
Additional advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of instrumentalities and combinations particularly pointed out in the appended claims.